martin



T. G. MARTIN.

TWO WIRE PARTY LINE LOCKDUT TELEPHONE SYSTEM.

APPLICATION FILED DEC. 1. ma.

1,324,202. Patented Dec. 9,1919.

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InuenIEu" T. G. MARTIN.

TWO WIRE PARTY LINE LOCKOUT TELEPHONE SYSTEM.

APPLICATION mm are. 1. ma.

3 SHEETS-SHEET 2- InuenIEr-- THZJUZEM'BPTZT'I.

Pmnmd Dec. 9,1919.

T. G. MARTIN. TWO Wm: PARTY LINE LOCKOUT TELEPHONE SYSTEM.

APPLICATION FILED DEC. 1. I Patented De 9 1919.

3 SjlEETS-SHEET 3.

N ED ES PATENT OFFICE.

TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC QOMfiIkHY, OF CHICAGO, ILLINOIS, A. GORPOBATION OF ILLINOIS.

' Ewe-WIRE PARTY-LINE LOCKOUT rnnnrnonn sYs'rEu.

Specification of Letters Patent.

Patented Dec. 9, 1919.

Original application filed January 3, 1911, Serial No. 600,610. Renewed April 29, 1918, Serial No. 281,539. Patent No. 1,291,587. Divided and this application filed December 7, 1918. Serial No. 265,813.

' To all whom it may concern.-

have inventeda certain new and useful Improvement in Two-Wire Party-Line Lookout Telephone Systems, of which the followin is a specification.

. y invention relates to telephone systems in eneral, and is illustrated in connection wit a party line such as is shown in my prior application Serial No. 231,539, filed April 29, 1918, renewal of Serial No. 600,610 issued as Patent No. 1,291,587, Jan. 11, 1919, of which this application is a divisioii.

The object oi this invention is to provide means whereby, it a call is set up to a called subscriber who answers the call but hangs up before conversation is completed, the calling subscriber may a ain signal or rering the called subscriber Without having to hang up and extend thecall again.

It is also an object to provide certain details and features of improvement and combinati'ons tending to increase the eilicicncy and serviceability of a telephone exchange system of this particular character. 7

To the foregoing and other useful ends my invention consists in matters hereinafter 'set forth and claimed.

In the accompanying drawings Figures .1 and 2 taken to ether show a complete circuit connection tween a calling substation A (Fig. 1) and a called substation A (Fig, 2) in a system embodying the principles of my invention.

Fig. '3 isgafdiagranunatic representation "of the essentialf' fatures of the so-called master switch 1) (Fig.1).

In Fig. 1 there is shown a party-line to which the two telephones A and A are connected. This line is connectedwith the individual or line switch C at the central of fice. A number of individual. switches C are controlled by a common master switch D and have common access to a group of trunk lines each of which leads to a selector similar to selector E. The selector E, together with a number of other similar switches, has common access to a number of rasses trunk lines leading to connector switces F (Fig;2)','which in turn have direct access to the calling terminals of the subscribers lines.

The line switches C and C and. master switch D are of thegeneral type disclosed in British Patent No. 26,301 of 1906, and in the American Telephone Journal of New York, N. Y. of June 6, 1908, having a somewhat modified construction. Referring to the line switch C, the operating windin -2, cut-011 winding 3, line winding 4, an auxiliary winding 111, are placed upon a single core forming a plural wound elcctromagnet having two distinct magnetic circuits, so that the wlndings upon one end have no efl'ect upon the armatures upon the other end. Of the windings upon the upper end of the magnet the winding 2 is strong enough to operate both the plunger arm 12 and cut-ofi armature 3, while the winding 3, though strong enough to operate the armature 5 and to hold the plunger arm 12 in its operated position, is not strong enough to attract said plunger arm from its normal position.

The selector E is of the general type (lisclosed United States Letters Patent No. 815,321,1ssued March13, 1906, to Keith,

Erickson and Erickson, being modified some- What, however, in order to operate in a twowire system, i. 6., a system in which thocentral ofiice apparatus is controlled by im pulses transmitted from the calling substation over the two sides of the line in series. The release magnet 105 is preferably arranged to release the switch mechanism immediately upon energizing in the manenr shown United States Letters Patent No. 815,176 for connector Switches, rather than upon'deen'er "Zing as shown in said selector Patent 0. 815,321. The relays 114, 51 and 38 denergize slowly when their energizing circuits are broken.

The connector F is of the general type disclosed in United States Letters Patent No. 815,176, issued March 13, 1906, to Keith, Erickson, and Erickson, but, like the selector, is modified to operate in a two-wire system, i r f The substations may be of any suitable common battery two-wire automatic type. The ones with which I have elected to illustrate my invention comprise the,

switch hook 7, transmitter 8 and ringer 9. For the purpose of producing impulses for controlling the central office apparatus, this substation is also provided with a pair of impulse springs 10 and 11, impulse wheel 18 and a dial (not shown).- A pair of springs 8 and 9 are provided for glosing a shunt circuit about the transmitter and receiver. In the preferred form of m invention I provide each substation with a relay which is adapted, when in an operated position, to close the contact between the sprin '14 and 15, thereby bridging the talking circuit across the line conductors. The relay is also provided with a spring 19 which, when the relay is energized, catches and locks the armature 20 in its operated position until the receiver hook is pulled down. Since the relay, when energized is locked up mechanically it cannot be affected by any change in the circuit conditions of the telephone, such as the opening of the line for the purpose of transmitting impulses to the central oflice. One terminal of the winding of the relay 13 is connected to the conductor '16, while the other terminal is connected to the hook switch spring 21 which normally engages the spring 22. As the switch hook rises when the receiver is removed, the spring 23 which is connected to the line conductor 17 engages the spring 22 and forces it out of engagement with the spring 21. Thus, for an instant durin the upward movement of the switch hoo all these springs 21, 22 and 23 are in contact, thereby momentarily bridging the relay 13 across the line. The relay 13 is so wound and adjusted that when it is thus bridged across the line it receives sufficient current from the central office to be operatively energized. If, however, the talking circuit of some other telephone is in bridge of the line at the time the circuit of the relay 13 is closed, sufficient current is shunted away from the relay by said talking circuit to prevent the relay from being operated. It will be understood that the relay 13 may have any suitable resistance, so as to secure its proper operation. Since the bridging of the talking circuit at a telephone across the line is dependent upon the operation of the relay 13 at that telephone, it will be seen that it will be impossible for a second subscriber to come in on the line while some other subscriber is using it. In case one subscriber wishes to call another subscriber on the same line, the first subscriber can, by pressing the button 25 and removing the short-circuit from the resistance 26, increase the resistance of his talking circuit sufliciently at the time the second subscriber removes his receiver to permit the relay 13 at the second substation to be energized and ace'the second telephone in talking conition.

In order to notify a calling subscriber whether or not the'line is busy when he attempts to make a call, I provide an opening in the wall of the telephone. Upon the end of the arm 28 of the receiver hook there is placed a small target or signal, which may have the word Busy written on it. When the receiver hook rises this target comes behind the opening 27 and maybe seen by the subscriber; T0 the am mature 20 there is attached an arm 29 carrying a shield 30 which, when the relay is energized, comes behind the opening 27, but in front of the target on the switch hook arm 28, thereby hiding said target from the calling subscriber.

The operations by which one subscriber calls another in the system shown herein are as follows: It will be assumed, first, that the subscriber at substation A calls subscriber A No. 220. lVhen the subscriber at substation A removes his receiver a momentary circuit is closed from ground G through the springs 31 and 32, line 17, springs 23, 22 and 21, relay 13, line 16, springs 34 and 33 and winding 4 to the battery lead 35, thence to battery B and to ground. The relay 13 is energized by this impulse and locks up, bridging the talking circuit across the line. The winding 4 of the switch C, upon energizing, attracts the armature 36, which closes the circuit of the winding 2. This circuit extends from ground G through the springs 31 and 1.10, windings 2 and 111, contact point 112 and armature 132 to the battery lead The winding 2, upon energizing, attracts the plunger arm 12 and cutoff armature 5. The lunger arm 12, upon being attracted, operates to force the line switch plunger into a bank of contact springs 113, 1M, 15, 41, 115, 116, 117 and 118, forcing them into contact in pairs as shown in the drawings. The armature 5, upon operating, disconnects the line winding 4 and ground G from the calling line, whereupon the armature 36 falls back and opens the circuit of the winding 2. Before the winding 2 is decnergized, however, a circuit is closed through the winding 3 in the following manner: "When the springs 113 and 117 are forced into contact with the springs 114 and 118 by the plunger ofthe line switch C, the line circuit is extended to the first selector switch E, and a circuit is closed from ground G through the lower winding of the relay 37 at the selector E, side switch wiper 119, springs 118 and 117, line 17, talking circuit of the springstd 41, 42, 43, 44 slide a d winding 3 of the switch'C tobattery. The winding 3 holds the switch C in its operated position after the armature 36 has fallen back and broken the circuit of the winding 2. In order to insure against the armature 36 falling back before the winding 3 is energized, the auxiliary1 windin 111 is energized inseries with t e pullown winding'2 and is short-cirouited through the I springs 121 and 122when the plunger arm reaches the limit of its downward move ment. The winding 111 thus serves to hold up the armature 36 for an instant after the winding 4 is denergized, so as to give the winding 3 a little longer time in which to energize. When the line switch C operates, the master switch D operates in a 7 wellknown manner to advance the plunger-s of the idle line switches to an idle trunk.

The operation of the master" switch D is as follows: The closure of contact between the springs 115 and 116 of the line switch C completes a circuit from ground Gr through the springs 115 and 116, contact point 123 (which is assumed to correspond to the trunk seized by the switch C), wiper 124, segment 165 and relay 125 to battery. The relay 125, upon energizing, closes a circuit through the relay 126. The relay 126, upon energizing, withdraws the pin 127 from an opening in the locking plate 128 and closes a circuit through the motor magnet 129. This circuit extends from ground G through the ma st 129, interrupter springs 130, contact point 131 and armature 132 to battery. The magnet 129 operates in a manner similar to that of aJbuzzer as long as the armature 132 engages the contact point 131, and, through the medium of the ratchet wheel 133 and link 134 (Fig. 3), rotates the plunger "shaft 135 about the shaft 136 to move the plungers of the idle line switches to an idle trunk line, As soon as the wiper 124, which moves with the plunger shaft, passes ofl the contact 123, the relay 125 deenergizes and breaks the circuit of the relay 126. The master switch continues to operate, however, until the next opening in the plate 128 passes directly under the in 127, whereupon the armature 132 falls back and breaks the circuit of the magnet 129. The openings in the plate are so spaced that the armature 132 can fall back only when the plunger-s of the line switches are directly in front of a trunk line. If busy trunk lines have to be passed before-the plungers can arrive at an idle trunk, the relays 125 and 126 are maintained energized by ground potentials on the master switch bank contacts of'said busy trunks until the idle trunk is reached.

' The calling subscriber now operates his calling device for the first digit 2 of the number desired, whereby the impulse springs 10 and 11 which are includedin the bridge atthe substation are separated twice momentarily, each time opening the line or inserting a high resistance therein and thereby causing the line relay 37 of the selector E to be deenergized. In order to eliminate the resistance of the transmitter and receiver from the line circuit, the short-circuit through thesprings 8 and 9 is closed at this time. This short circuit can be closed in an desired manner, butis preferablyplace un;- der the control of the calling device, so that when the calling device is operated, the springs 8 and 9 are brought into contact to close this short-circuit. The relay 37 upon deenergizing, closes a circuit from ground Gr through the springs 46, 48, 49 and 50 (the slow-acting relay 38 does not fall during the momentary interruption of its circuit), relay 51, vertical magnet 52 and side switch wiper 53 to battery. The vertical magnet operates to raise the switch shaft two steps, while the slow-acting relay 51 operates to close the circuit of the private magnet 54. The relay 51 does not have time to deenergize until after the last impulse for the digit is delivered, when it breaks the circuit of the magnet 54, which deenergizes and allows the side switch to pass to second position. The rotary magnet 55 thereupon operates in a well-known manner to rotate the wipers onto an idle trunk lead- I ing to a connector F, after which the side swltch of the selector passes to third position, cutting ofi' the line relay of the selector, and extending the line to the line relays 56 and 57 of the connector, whereupon said relays become energized. The energizing circuit for these relays extends from ground Gr through the relay 57, trunk conductor 137, thence over the heavy conductors through theselector E, line switch C, substatitan-ii and'backover the other side of the line through the switches C and E, trunk conductor 138 and relay 56 to battery. The relay 57 of the connector, upon energizing, completes a circuit from ground G through the springs 58 and 59, 60 and 61 and relay 62 to battery. The relay 62, upon energizing, extends a connection from ground G throughthe side switch wiper 63 and springs 64 and 65'to the conductor 66, for the purposeofprovidingja guarding potential for the: seieetor 'private bank contacts of the seized trunk, andfor maintaining a holding circuit for the relay 38 of the selector E.

passes to third position, and through the medium. of the springs 145 and 1&3 providesarguarding potential for the selector private. bank contacts during the short interval before the relays 5 7 and 62 of the connector operate. Of course, the relay 14A: deenergizes more quickly than does the relay 38 so as to close the above-described holding circuit before the latter relay drops back.

\Vhen the calling subscriber operates his calling device for the second digit 2, the line is again opened twice, each time breaking the circuit of the relays 56 and 57 at the connector. The slow relay 62 does not have time to fall back during the momentary interruption ofits circuit by the relay 57 consequently, each time the relay 56 deenergizes, a circuit is closed from ground Gr through the springs 67, 68, 69 and 70, relay 71, vertical magnet 72 and side switch wiper 73 to battery. The magnet 72 operates to raise the shaft and wipers two steps, while the slow-acting relay 71 acts in the same manner as explained for the relay 51 of the selector E to cause the private magnet 74 to trip the side switch to second position. In passing from first to second po sition, the side switch wiper 73 transfers the battery connection from the vertical magnet to the rotary magnet 75. When the calling device is operated for the last digit 0 the rotary magnet receives ten impulses and rotates the wipers ten steps onto the contacts of the line #220, after which the side switch is tripped to third position by the private magnet in the same manner in which it, was tripped to second position after the completion of the impulses for the first digit. The operating circuit of the retary magnet 7 5 extends from ground G through the springs 67 and 68, 69 and 70, relay 71, springs 14:6 and 1 17, magnet 75 and side switch wiper 73 to battery. 'VVhen the side switch reaches third position the connection between the calling and the called lines is completed, the called line is provided with a guarding potential at the connector private bank contacts, the line winding of the line switch C is cut off and a circuit is closed through the ringing relay 76. The switch C is cut oil by the winding 77, which is energized over a circuit extending from ground G through the side switch wiper 78, private wiper 79 and winding 77 to battery. The energizing circuit of the relay 76 extends from ground G through the interrupter 80, springs 81 and 82, relay 76 and side switch wiper 73 to battery. The relay 76 is energized intermittently to ring the called subscriber. The ringing circuit extends from one terminai of the ringing current generator N through the springs 148 and 149, side switch wiper 150, shaft wiper 151, line 152, substation springs 153' and 154, ringer and condenser 155, line 156, springs 157 and 158, wiper 159 and springs 160 and 161 to the other terminal of the'generator. then the receiver at the called substation is removed, that substation is provided with talking current through the back-bridge relay 83 of the connector. This circuit over which the talking current is supplied extends from ground Gr through the side switch wiper 78, lower winding of the relay 63, ringing relay springs 162 and 149, side switch wiper 150, line wiper 151, thence over the heavy conductors to and through the substation A and back over the other side of the line, and through the ringing relay springs 160 and 163, springs 164 and 165, upper windin ofthe relay 83 and side switch wiper T3 to battery. The relay 83, upon energizing, closes a circuit from ground G t-hrough the springs '67 and 81 of the relay 56, springs 85 and 86, relay 87 and side switch wiper 7 3 to battery. The relay 87, upon energizing, breaks the op erating circuit of the relay '76 and closes a locking circuit for itself through the springs 88.

The two connected subscribers may now carry on an uninterrupted conversation, and no other subscriber on either line can break in on the, connection. Referring to Fig. 1 suppose the receiver at substation A is removed. As the hook goes up a circuit will be closed through the relay 13 at that station but said relay will be shunted by the talking circuit at the substation A and will not be operated, thereby leaving the talking circuit open as shown in Fig. 1.

In case the called line had been busy when the connector F sought to make connection therewith, the private wiper 79 would have found its private bank contact. grounded and immediately upon engaging said contact would have extended a ground potential through the sideswitch wiper 78 (in second position), sprin s 90 and 89 and lower winding of the re ay 91 to the sprin 92 of the private magnet relay 71 an through the, private magnet 74 to battery. As the relay 71 denergized after the last digit was called, the private magnet would have been maintained energized over the above circuit by the ground at the private wiper, locking the side switch in second position and at the same time the relay 91 would have been energized. This relay, upon energizing, transfers the holding ground for the private magnet from the guarded private bank contact to the ground G through the side switch wiper 63 and springs 64 of relay 62. The side switch being locked in second position, no connection would be completed with the busy line, and

eennededswith; the calling line by the .010 sure of th springs 95 at the relay 91. .7 V

From the int-ageing it. evident: that the connector cannotiiniake connection with a lineiwhich has a ground upon its "connector private bank contacts. It will also be seen that as soon the connection is extended to the, selectorE a guarding potential is extended from ground Gr through, the springs alhal, 42, a3, 44 andAE, and over the conduetor 96 to the connector private, bank contacts of the calling line. In order tor'permitiallsubscriber to: call back on 'his own line to signal another subscriber thereon, each trunk line leading to a selector E is provided with the relays 97 and 98, which so modify the guarding potential of the calling line while the calling device at the calling station is being operated as to allow a connector to make connection therewith at that time. It will be seen that all impulses must pass through the relay 97 which, upon denergizing after connection is extended to the selector E, closes a circuit through the slow-acting relay 98. The relay 98, upon energizing, removes the shortcircuit around the resistance 99, thereby inserting this resistance in the ground connection to the rivate contacts of the calling line. Thus it will be seen that when the calling subscriber is calling back on his own line, at the time the private magnet relay 71 denergized after the last digit is called, the resistance 99 will be included in the circuit, which tends to lock the private magnet. This resistance is high enough to prevent said magnet from being locked, and the side switch passes to third position in the usual manner. A moment later the relay 98 (Fig. 1) falls back and cuts out the resistance 99 'to restore the guarding potential of the calling line to its effective condition.

When a calling subscriber calls back on his own line a circuit will be closed through the back-brid e relay of the connector and the calling su station, which will cause the circuit of the ringer relay 76 to be opened. In order to signal the called substation the calling subscriber must press the button 25, thereby increasing the resistance of the bridge sufliciently to allow the connector line relay 56 to fall back, but not the relay 57. The relay 56, upon falling back, breaks the circuit of the relay 87 which falls back and closes the circuit of the ringer relay. The pressing of the button 25 also increases the resistance of the bridge at substation A sufficiently to allow the relay 13 at the called substation to be energized when the called subscriber answers. The bridging of the called telephone across the line causes the relay 56 to again pull up, which causes the ringing current to be cut ofl. The calling subscriber then releases his button.

After a connection. ISLGOHlPlBtBd. the

switches are .releasedbythe hanging u of the receiver at the calling substation. his allows the connector line relays to fall back, which removestheholding round from the release relays 62 and 38 o the switches F and E, respectively. The relay 62, upon denergizing, completes the circuit of the release magnet 10l,'which releases the connector. The circuit of the magnet 101 is broken at the springs 102 and 1031 when the switch shaft reaches its lowest position In like manner the selector E is released b the magnet 105 when therelay: 38 falls ack. When the relay 38 deenergizes it also breaks the holding circuit of the winding 3 of the switch C, allowing its plunger to be restored.

In the case of a call from the subscriber A for instance to the subscriber, should the subscriber A hang up his receiver before the subscriber A had finished his conversation the circuit is so arranged that the calling subscriber may then operate his calling device to again operate the bell at station A In this drawing (Fig. 2) it will be noticed that the ring cut-ofl" relay 87, after the called man hangs up and deenergizes relay 83 is locked energized only through the springs 67 and 84 of the line relay 56, instead of being permanently locked. Now when the calling subscriber operates his dial and relay 56, in response to the resultant opening of the line circuit, falls back, this locking circuit of relay 87 is opened at springs 67 and 84 and relay 87 therefore falls back and closes the original circuit of the ringing relay 7 6 again. Relay 76 operates in the same manner as when the call was first set up to connect the enerator N to the called line to signal t. e subs riber thereon. Relay 83 will again be energized as soon as the called subscriber answers this second call and 'again energizes relay 87 through springs 85 and 86. It will thus be seen that a subscriber is saved the trouble of hanging up and again setting up the connection to the subscriber A in case the subscriber A hangs up too soon.

In party-line systems of the kind shown herein, the different parties on a line may be signaled selectively in the following wellknown manner: The bells of the different substations may be tuned or otherwise adapted to respond to only a certain kind of ringing current. Each subscribers line may be accessible by a plurality of groups of connectors, each group representing a difi'erent hundreds digit. The numbers of the different substations on the same line may then be given different hundreds digits, corresponding to the respective hundreds groups of connectors. Each group of connectors may be supplied with ringing current of the proper character to operate only the ringersof the substations whose hundreds digits correspond to that connector group. Thus,to si al any particular substation on a line t e line must be called through a connector in a group which is supplied with ringing current of the proper character to operate the bells at the desired substation, and the connector group is determined by the hundreds digit of the called substation.

Throughout this specification, where a telephone is spoken of as being in normal position, it is meant that the receiver is on the switch hook. A line is spoken of as being in normal position when the receivers of all telephones on said line are on their switch hot) 9.

What I claim as my invention is:

In a telephone exchange system, a plurality of lines, automatic means forestablishing a connection between a calling and a called line, automatic means operative as a result of the establishment of the connection for ringing called lines, a switch for producing interruptions in said calling line, and means responsive to said interruptions for reringin called lines. 7

Signs by me at Chicago, Illinois, this 2d day of December, 1918.

TALBOT G. MARTIN, 

